The invention relates to a device for continuous drying of a pulp web, particularly a tissue web, with a drying drum and an air circulating system, where the drying drum has a cylindrical shell designed as a honeycombed body.
In conventional tissue plants, the drying process begins at an ingoing dryness of some 40 to 45%. In order to achieve higher paper volume, papermakers now dispense with preliminary mechanical dewatering, and the ingoing dryness of this newer type of device is around 20 to 25%. These plants operate with through-air drying. During the heating process, one or more consecutive through-air drying drums at ambient temperature are exposed abruptly to the supply air temperature of approximately 300° C. The drying drums currently in use have a thin-walled shell, for example a perforated or honeycombed body, that is joined to thick-walled end flanges. Due to the substantial differences in mass between drum shell and end flange, there is excessive stress at the transition points that leads to deformation and even structural damage. The same damage occurs if the drums are cooled down abruptly from operating to ambient temperature during an emergency shutdown, when they are sprayed with cold water in order to prevent the plastic wires enclosing the drums from being damaged.